Vehicle control method and vehicle control device

ABSTRACT

A vehicle control method for controlling a vehicle using a vehicle control apparatus includes: a sensor configured to detect a state outside a subject vehicle; and a control device. The vehicle control method includes: executing control of recovering a travel trajectory of the subject vehicle to a target trajectory, as ordinary control, by giving a steering amount in a lateral direction with respect to a travel lane of the subject vehicle; using detection data of the sensor to determine whether or not another vehicle is traveling in an adjacent lane to the travel lane of the subject vehicle; and when determining that the other vehicle is traveling in the adjacent lane ahead of the subject vehicle, increasing a response of the steering amount to a higher response than that in the ordinary control, before the subject vehicle passes the other vehicle.

TECHNICAL FIELD

The present invention relates to a vehicle control method and a vehiclecontrol apparatus.

BACKGROUND

A vehicular steering device having an electric motor for steering isknown (see JP2015-37932A, for example). When the vehicle is in a stateof traveling straight ahead, the driving power relating to the electricmotor is controlled on the basis of vehicle information including thesteering torque and steering angle, and assist torque is thereby givento the steering system. The vehicular steering device as disclosed inJP2015-37932A operates to calculate an integration value of torquedetermined by integrating the steering torque and, when the integrationvalue of torque is not less than a threshold, perform steering-pullreduction control for the driving power relating to the electric motorso as to cancel a steering-pull phenomenon of the vehicle.

SUMMARY

However, there is a problem in that it takes time until thesteering-pull reduction control is started after the vehicle causes thesteering pull because the steering-pull reduction control is startedwhen the vehicle causes the steering pull and the integration value ofsteering torque becomes the threshold or more.

A problem to be solved by the present invention is to provide a vehiclecontrol method or a vehicle control apparatus with which control ofsuppressing a phenomenon that the subject vehicle is attracted toanother vehicle when passing the other vehicle can be executed in ashorter time as compared with the case of executing the steering-pullreduction control at the time point when the integration value ofsteering torque becomes a threshold or more as in the prior art.

The present invention solves the above problem through: executingcontrol of recovering a travel trajectory of the subject vehicle to atarget trajectory, as ordinary control, by giving a steering amount in alateral direction with respect to a travel lane of the subject vehicle;using detection data of a sensor to determine whether or not anothervehicle is traveling in an adjacent lane to the travel lane of thesubject vehicle; and when determining that the other vehicle istraveling in the adjacent lane ahead of the subject vehicle, increasinga response of the steering amount to a higher response than that in theordinary control, before the subject vehicle passes the other vehicle.

According to the present invention, an effect can be obtained in whichthe attraction suppression control can be executed in a short time.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block diagram of a vehicle control system 1000 having avehicle control apparatus according to one or more embodiments of thepresent invention;

FIG. 2 is a flowchart illustrating a control procedure of a steeringcontrol process executed by the vehicle control system according to oneor more embodiments of the present invention;

FIG. 3 is a diagram illustrating the positional relationship between theimaging range of a camera and another vehicle in the vehicle controlsystem according to one or more embodiments of the present invention;

FIG. 4 is a diagram illustrating the positional relationship between thesubject vehicle and another vehicle in the vehicle control systemaccording to one or more embodiments of the present invention;

FIG. 5 is a block diagram of steering control executed by a controldevice in the vehicle control system according to one or moreembodiments of the present invention;

FIG. 6 is a diagram illustrating the positional relationship between thesubject vehicle and another vehicle in the vehicle control systemaccording to one or more embodiments of the present invention;

FIG. 7 is a graph illustrating the steering amount characteristics inthe vehicle control system according to one or more embodiments of thepresent invention; and

FIG. 8 is a diagram illustrating the positional relationship between thesubject vehicle and another vehicle in the vehicle control systemaccording to one or more embodiments of the present invention.

DETAILED DESCRIPTION

Hereinafter, one or more embodiments of the present invention will bedescribed with reference to the drawings. In the embodiments, anexemplary case will be described in which the vehicle control apparatusaccording to the present invention is applied to a vehicle controlsystem for vehicles.

FIG. 1 is a block diagram of a vehicle control system 1000 having avehicle control apparatus 100 according to one or more embodiments ofthe present invention. The vehicle control system 1000 according to oneor more embodiments of the present invention includes a steering unit 1,a steering wheel 2, wheels 3 and 4, and the vehicle control apparatus100. The vehicle control apparatus 100 according to one or moreembodiments of the present invention controls steering of the wheels 3and 4 in response to the operation of the steering wheel 2.

The steering unit 1 has a shaft 11, a motor 12, a steering angle sensor13, a torque sensor 14, and a gear (not illustrated). The shaft 11 isconnected to the right and left drive wheels. A rack-and-pinion-typesteering gear is used for the gear, and the front wheels 3 and 4 aresteered in accordance with the rotation of the shaft 11.

The motor 12 is, for example, a brushless motor, and the output shaft ofthe motor 12 is connected to the rack gear via a reduction gear andoutputs the steering torque for steering the front wheels 3 and 4 to therack in response to a control command from a control device 30. Themotor 12 also operates to give a steering amount in response to thecontrol command from the control device 30 and outputs the steeringtorque. The steering amount is given to the steering unit 1 in order topromote steering for disturbance suppression. For example, when adisturbance such as a crosswind is input and affects the behavior of thevehicle, the steering torque for the disturbance suppression is given tothe steering thereby to suppress the steering operation in the directionin which the crosswind blows. Such steering-pull control for the vehicledue to disturbance is employed, for example, in a lane departureprevention assistance system and other similar systems. When thesteering mechanism of the steering unit 1 can be electronicallycontrolled, the motor 3 may be installed so as to generate a steeringamount directly to the steering mechanism. When the steering unit 1 isconfigured for electrohydraulic power steering, the motor 3 supplies thepower to an electric pump. The motor 12 corresponds to the “actuator” ofthe present invention.

The steering angle sensor 13 detects the rotation angle of the motor 12to calculate the steering angle of the front wheels 3 and 4. There is acorrelation between the rotation angle of the motor 12 and the steeringangle of the front wheels 3 and 4. The steering angle sensor 13calculates the steering angle corresponding to the motor rotation anglewhile referring to a map that represents the correspondence relationshipbetween the rotation angle of the motor 12 and the steering angle of thefront wheels 3 and 4, and thereby detects the steering angle of thefront wheels 3 and 4.

The torque sensor 14, which is provided in a connection mechanism thatconnects the steering wheel 2 and the steering unit 1, detects thesteering torque corresponding to the steering amount of the steeringwheel 2 operated by the driver. The steering angle sensor 13 and thetorque sensor 14 output the detected values to the control device 30.

A camera 20 is provided as an imaging device that images a state aheadof the vehicle. The camera 20, which operates while the vehicle istraveling, is used as a sensor that detects the surroundings of thevehicle. The camera 20 outputs the data of captured images to thecontrol device 30. The sensor which performs detection ahead of thevehicle is not limited to the camera 20 and may also be radar, sonar, orother similar device. In addition or alternatively, for example, thesubject vehicle may acquire information on other vehicles usingvehicle-to-vehicle communication thereby to detect the state ahead ofthe subject vehicle.

The vehicle control apparatus 100 includes the motor 12, the steeringangle sensor 13, the torque sensor 14, the camera 20, and the controldevice 30. These components of the vehicle control apparatus 100 areconnected to one another via a controller area network (CAN) or otheronboard LAN to mutually exchange information. The vehicle controlapparatus 100 executes the steering control on the basis of thedetection data which is input from the steering angle sensor 13 and thetorque sensor 14. When a shift occurs between the steering amount of thesteering wheel 2 and the actual steering angle detected by the steeringangle sensor 13, the vehicle control apparatus 100 calculates a controlsteering amount such that the steering angle detected by the steeringangle sensor 13 coincides with the steering amount of the steering wheel2, and outputs a control command value corresponding to the controlsteering amount to the motor 12.

The control device 30 of the vehicle control apparatus 100 according toone or more embodiments of the present invention is a specific computercomprising a ROM 32 that stores a vehicle control program, a CPU 31 asan operation circuit that executes the program stored in the ROM 32 toserve as the vehicle control apparatus 100 according to one or moreembodiments of the present invention, and a RAM 33 that serves as anaccessible storage device.

The vehicle control program according to one or more embodiments of thepresent invention is a program for execution of a control procedure thatincludes detecting a state around the vehicle, executing steeringcontrol of the vehicle in accordance with the detection result, andgenerating a lateral movement of the vehicle. This program is executedby the control device 30 of the vehicle control apparatus 100 accordingto one or more embodiments of the present invention.

The control device 30 of the vehicle control apparatus 100 according toone or more embodiments of the present invention involves an ambientsituation detection process, a calculation function of calculating acontrol command value for giving a steering amount, and a function ofexecuting a steering control process. The control device 30 executeseach of the above processes and functions by cooperation of software forrealizing each process or function and the above-described hardware.

Here, a phenomenon will be described that the subject vehicle isattracted to another vehicle when passing the other vehicle. The othervehicle is, for example, a large-sized car, and the classification oflarge-sized cars can be preliminarily determined, for example, by thevehicle weight and the like. The large-sized car is a vehicle withwhich, for example, when the subject vehicle travels on the side of thelarge-sized car, a phenomenon occurs that the subject vehicle isattracted to the large-sized car. Large-sized cars are vehicles such asbuses and trucks.

It is assumed that the subject vehicle and the other vehicle travel, forexample, on a straight expressway. The traveling conditions of thesubject vehicle and the other vehicle are as follows. The other vehicleis traveling in the left-side lane while the subject vehicle istraveling in the right-side lane (overtaking lane). The other vehicletravels ahead of the subject vehicle 40 and the vehicle speed (V1) ofthe subject vehicle 40 is higher than the vehicle speed (V2) of theother vehicle, so that the subject vehicle comes close to the othervehicle with time.

When the subject vehicle comes close to the other vehicle from behind,the other vehicle is traveling on the left ahead of the subject vehiclein a state of being close to the subject vehicle. At this time, a flowrate difference occurs between the air flowing to the left and rightwith respect to the subject vehicle. When, in the traveling direction ofthe subject vehicle, the airflow closer to the other vehicle is A_(L)and the airflow farther from the other vehicle is A_(R), the flow rateof the airflow (A_(L)) is lower than the flow rate of the airflow(A_(R)).

As such, when the subject vehicle comes close to the other vehicle andthe subject vehicle travels to pass by the other vehicle, the subjectvehicle is attracted to the other vehicle side (this phenomenon willalso be referred to as an “attraction phenomenon,” hereinafter). Whenthe driver of the subject vehicle perceives the attraction phenomenon tothe other vehicle, the driver operates the steering wheel 2 so as to getaway from the other vehicle. At this time, the steering wheel 2 receivesthe steering force in the direction of coming close to the othervehicle; therefore, to generate the reaction force to the steeringforce, the steering torque has to be increased.

Provided that the attraction phenomenon is a disturbance, it is alsoconceivable to utilize a lane departure prevention assistance system torecover the travel trajectory of the subject vehicle to a targettrajectory (linear trajectory). In the steering control used in the lanedeparture prevention assistance system, however, the steering control isexecuted when the subject vehicle receives a disturbance and the systemdetects that the subject vehicle is attracted to the other vehicle.Thus, it takes time until the control for suppressing the attractionphenomenon is executed after the system detects the attractionphenomenon. The vehicle control apparatus 100 according to one or moreembodiments of the present invention executes the control forsuppressing the attraction phenomenon in a short time by the vehiclecontrol method, which will be described below.

FIG. 2 is a flowchart illustrating a control procedure of the steeringcontrol process executed by the vehicle control system 1000 according toone or more embodiments of the present invention. The control flowillustrated in FIG. 2 is repeatedly executed at a predetermined cycle.

In step 1, the control device 30 acquires an image captured by thecamera 20. FIG. 3 is a diagram illustrating the positional relationshipbetween an imaging range P of the camera 20 and another vehicle 50. Thecamera 20 is installed at the front part of the subject vehicle 40. Forexample, the camera 20 is installed in the vicinity of the center abovethe windshield. As illustrated in FIG. 3, when the other vehicle 50 istraveling in an adjacent lane ahead of the subject vehicle 40, the othervehicle 50 is included in the imaging range of the camera 20.

In step 2, the control device 30 determines whether or not a passingflag is in the OFF state. The passing flag, which represents a valuethat indicates whether or not the subject vehicle 40 is about to pass alarge-sized car, is stored in a memory (not illustrated) of the controldevice 30. When the subject vehicle 40 is about to pass a large-sizedcar, the passing flag is turned on. The passing flag is turned on whensatisfying a passing condition that is preliminarily set. Thedetermination as to whether the passing condition is satisfied isexecuted before the subject vehicle actually passes the other vehicle asan object to be passed.

When the passing flag is in the OFF state, the control flow of step 3 isexecuted. On the other hand, when the passing flag is in the ON state,the control flow of step 9 is executed.

The passing condition is defined by the size of another vehicletraveling ahead of the subject vehicle, the positional relationshipbetween the subject vehicle and the other vehicle, and the relativespeed of the subject vehicle to the other vehicle. The flow fordetermining whether or not the passing condition is satisfiedcorresponds to the control flow of step 3 to step 7.

In step 3, the control device 30 determines whether or not a large-sizedcar is present in an adjacent lane ahead. Specifically, the controldevice 30 acquires an image captured by the camera 20 and specifies avehicle image from the captured image. The vehicle image is an imagewhen viewed from behind the vehicle. The control device 30 measures thearea of the vehicle image. The size of the vehicle image corresponds tothe area of the vehicle image. The control device 30 compares the areaof the vehicle image with an area threshold representing a large-sizedcar and, when the area of the vehicle image is larger than the areathreshold, determines that the vehicle ahead is a large-sized car. Whenthe control device 30 determines that a large-sized car is present inthe adjacent lane ahead, the control flow of step 4 is executed. On theother hand, when the control device 30 determines that no large-sizedcar is present in the adjacent lane ahead, the control flow of step 15is executed. Criteria for the control device 30 to determine whether ornot a large-sized vehicle is present may include not only the size ofthe vehicle image but also the distance between the subject vehicle andanother vehicle, the relative speed of the other vehicle to subjectvehicle, etc.

In step 4, the control device 30 uses the image captured by the camera20 to calculate the positional relationship between the subject vehicleand the other vehicle and the relative speed of the other vehicle to thesubject vehicle. The camera 20 sequentially captures images ahead of thesubject vehicle at a predetermined cycle. The control device 30 obtainsa difference between the sequentially captured images and calculates arelative speed (V_(ref)) from the difference and the current vehiclespeed of the subject vehicle.

FIG. 4 is a diagram illustrating the positional relationship between thesubject vehicle and another vehicle. As illustrated in FIG. 4, the othervehicle 50 is traveling in an adjacent lane ahead of the subject vehicle40. The center point O of the subject vehicle 40 is the point of origin,the traveling direction of the subject vehicle 40 is the x-direction,and the lateral direction is the y-direction. The lateral direction ofthe subject vehicle is a direction orthogonal to the traveling directionof the subject vehicle 40 on the road surface. The control device 30specifies a rear end Z_(b) of the other vehicle 50 from the imagecaptured by the camera 20. The rear end Z_(b) is a vertex closest to thesubject vehicle 40 among vertices on the four corners when the othervehicle 50 is viewed from directly above. As illustrated in FIG. 4, whenthe other vehicle 50 is traveling on the left side ahead of the subjectvehicle 40, the rear end Z_(b) is a point positioned at the lower rightwhen the other vehicle 50 is viewed from directly above. The controldevice 30 also specifies a front end Z_(a) of the subject vehicle. Thefront end Z_(a) is a vertex closest to the other vehicle 50 amongvertices on the four corners when the subject vehicle 40 is viewed fromdirectly above. The positions of the front end Z_(a) and the rear endZ_(b) can be represented by position coordinates with the center point Oas the point of origin.

The control device 30 calculates an inter-vehicle distance in thex-direction and an inter-vehicle distance in the y-direction. Theinter-vehicle distance x_(ref) in the x-direction represents a length(longitudinal length) of the x-component of the distance from the frontend Z_(a) of the subject vehicle to the rear end Z_(b) of the othervehicle, and the inter-vehicle distance y_(ref) in the y-directionrepresents a length of the y-component (lateral length) of the distancefrom the front end Z_(a) of the subject vehicle to the rear end Z_(b) ofthe other vehicle.

The control device 30 also calculates a shift amount (amount ofdeviation) (y_(d)) in the y-direction. The shift amount represents themagnitude of a shift with respect to the center line C of the travellane of the subject vehicle 40. The center line (lane center line) C isa line located on the center of a boundary line (white line) thatdivides the travel lane. The shift amount (y_(d)) is a distance betweenthe center line C and the x-axis. The larger the shift amount (y_(d)),the shorter the lateral approach distance between the subject vehicle 40and the other vehicle 50. When the other vehicle is present on the leftside of the subject vehicle, the shift amount (y_(d)) takes a positivevalue in the direction leftward from the center line C. When the othervehicle is present on the right side of the subject vehicle, the shiftamount (y_(d)) takes a positive value in the direction rightward fromthe center line C. The shift amount (yd) being larger than zero meansthat the subject vehicle is closer to the other vehicle than the centerline C.

In step 5, the control device 30 compares the lateral inter-vehicledistance (y_(ref)) with a first distance threshold (y_(th_a)) todetermine whether or not the lateral inter-vehicle distance (y_(ref)) isless than the first distance threshold (y_(th_a)). The first distancethreshold (y_(th_a)) is a threshold for determining that the lateralspacing between the subject vehicle and the other vehicle is small. Thefirst distance threshold (y_(th_a)), which represents a length in they-direction, is a threshold that is preliminarily set. When the lateralinter-vehicle distance (y_(ref)) is less than the first distancethreshold (y_(th_a)), the control device 30 executes the control flow ofstep 6. When the lateral inter-vehicle distance (y_(ref)) is not lessthan the first distance threshold (y_(th_a)), the control device 30determines that there is no other vehicle with a short inter-vehicledistance in the lateral direction of the subject vehicle, and executesthe control flow of step 15.

In step 6, the control device 30 compares the inter-vehicle distance(x_(ref)) in the traveling direction with a second distance threshold(x_(th_a)) to determine whether or not the inter-vehicle distance(x_(ref)) in the traveling direction is less than the second distancethreshold (x_(th_a)). The second distance threshold (x_(th_a)) is athreshold for determining that the spacing in the traveling directionbetween the subject vehicle and the other vehicle is small. The seconddistance threshold (x_(th_a)), which represents a length in thex-direction, is a threshold that is preliminarily set. When theinter-vehicle distance (x_(ref)) in the traveling direction is less thanthe second distance threshold (x_(th_a)), the control device 30 executesthe control flow of step 7. When the inter-vehicle distance (x_(ref)) inthe traveling direction is not less than the second distance threshold(x_(th_a)), the control device 30 determines that no other vehicle witha short inter-vehicle distance in the traveling direction of the subjectvehicle is present in an adjacent lane, and executes the control flow ofstep 15.

In step 7, the control device 30 compares the relative speed (V_(ref))with a relative speed threshold (V_(th)) to determine whether or not therelative speed (V_(ref)) is higher than the relative speed threshold(V_(th)). The relative speed threshold (V_(th)) is a determinationthreshold that indicates that the subject vehicle continues to comeclose to the other vehicle with time. The relative speed threshold(V_(th)) is a threshold that is preliminarily set. When the relativespeed (V_(ref)) is higher than the relative speed threshold (V_(th)),the control device 30 executes the control flow of step 8.

That is, when there is another vehicle with short inter-vehicledistances in the x-direction and y-direction of the subject vehicle andthe subject vehicle is coming close to the other vehicle from behindwith time, the control device 30 determines that the passing conditionis satisfied. On the other hand, when the relative speed (V_(ref)) isnot higher than the relative speed threshold (V_(th)), the controldevice 30 determines that the subject vehicle is not coming close to theother vehicle with time, and executes the control flow of step 10.

In step 8, the control device 30 switches the passing flag from OFF toON. In step 9, the control device 30 uses the image captured by thecamera 20 to calculate the positional relationship between the subjectvehicle and the other vehicle and the relative speed (V_(ref)) of theother vehicle to the subject vehicle. The positional relationshipbetween the subject vehicle and the other vehicle is represented by theinter-vehicle distance (x_(ref)) in the traveling direction and theinter-vehicle distance (g_(ref)) in the lateral direction. When thecontrol flow of step 9 is executed immediately after the passing flag isturned on, the positional relationship (x_(ref), y_(ref)) between thesubject vehicle and the other vehicle, the shift amount (y_(d)), and therelative speed (V_(ref)), which are calculated in the control flow ofstep 4, may be used.

In step 10, the control device 30 calculates a passing completion time(t_(end)) using the positional relationship (x_(ref)) and the relativespeed (V_(ref)). The passing completion time (t_(end)) can be obtained,for example, through adding the inter-vehicle distance (x_(ref)) in thetraveling direction to the length of the other vehicle in thex-direction and dividing the obtained value by the relative speed(V_(ref)).

In step 11, the control device 30 compares an elapsed time (t_(d)) fromthe time when the passing flag is turned on with the passing completiontime (t_(end)). When the elapsed time (t_(d)) is less than the passingcompletion time (t_(end)), the control device 30 determines that passinghas not been completed, and executes the control flow of step 12. On theother hand, when the elapsed time (t_(d)) is not less than the passingcompletion time (t_(end)), the control device 30 determines that passinghas been completed, and executes the control flow of step 13. In thecontrol flow of step 13, the control device 30 switches the passing flagto the OFF state.

In step 12, the control device 30 calculates an approach distance(L_(ref)) between the subject vehicle and the other vehicle and comparesthe approach distance (L_(ref)) with a third distance threshold(L_(th)). The approach distance (L_(ref)) corresponds to a distance fromthe front end Z_(a) of the subject vehicle to the rear end Z_(b) of theother vehicle. The approach distance (L_(ref)) is a threshold fordetermining that the subject vehicle is coming close to the othervehicle from behind. When the approach distance (L_(ref)) is less thanthe third distance threshold (L_(th)), the control device 30 executesthe control flow of step 14. When the approach distance (L_(ref)) is notless than the third distance threshold (L_(th)), the control device 30executes the control flow of step 13. In step 13, the control device 30turns off the passing flag. Then, the control device 30 executes thecontrol flow of step 15.

In step 14, the control device 30 compares the shift amount (y_(d)) witha fourth distance threshold (y_(d_th)). The fourth distance threshold(y_(d_th)) is a threshold for determining whether or not the subjectvehicle is closer to the other vehicle side than the center line C ofthe travel lane. The fourth distance threshold (y_(d_th)) is a value ofzero or more. When the shift amount (y_(d)) is larger than the fourthdistance threshold (y_(d_th)), the control device 30 executes thecontrol flow of step 16. On the other hand, when the shift amount(y_(d)) is not larger than the fourth distance threshold (y_(d_th)), thecontrol device 30 executes the control flow of step 15.

In step 15, the control device 30 sets an integral increase gain (k_(i))to an ordinary gain. The ordinary gain is one. In step 16, the controldevice 30 sets the integral increase gain (k_(i)) to an increased gain.The increased gain has a value larger than one. In step 17, the controldevice 30 executes the operation control using the integral termincrease gain which is set in step 15 or step 16.

Details of the control flow from step 15 to step 17 will be describedwith reference to FIG. 5. FIG. 5 is a block diagram of the steeringcontrol. FIG. 6 is a diagram illustrating the positional relationshipbetween the subject vehicle and another vehicle.

The control device 30 has an input of a command value (y_(cr)) of theshift amount and an output of a steering control amount (δ_(conf)). Thesteering control amount (δ_(conf)) is represented by a steering torquecommand value required to generate the steering amount. The steeringtorque command value is input to the steering unit 1, which outputs thesteering amount (steering torque) corresponding to the command value. K1represents a transfer element when the command value (y_(cr)) of theshift amount is the input and the steering amount is the output. K2represents a transfer element when a difference (Δy) is the input andthe steering amount is the output. The difference (Δy) is a difference(Δy_(d)) between the command value (y_(cr)) of the shift amount and ashift amount (y_(d_0)) that is detected by the sensor. k_(i) representsthe integral increase gain.

The command value (y_(cr)) of the shift amount is a target value formoving the subject vehicle 40 in the lateral direction in order that thetravel trajectory of the subject vehicle 40 coincides with the targettrajectory of the subject vehicle 40 when the position of the subjectvehicle 40 is shifted with respect to the center line C of the travellane. The travel trajectory of the subject vehicle represents atrajectory on the route along which the subject vehicle actuallytravels. The target trajectory is a trajectory of travel that is to be atarget when the subject vehicle travels by automated or autonomousdriving or the like. The target trajectory can be obtained, for example,using an image captured by the camera 12 or the like. The control device30 calculates the steering control amount (δ_(conf)) for the commandvalue (y_(cr)) of the shift amount using a transfer function illustratedas the block diagram of FIG. 5. The steering unit 1 outputs the steeringtorque for the input of the steering control amount (δ_(conf)). Inpractice, the output of the steering unit 1 is the steering torque forthe front wheels 3 and 4, but for descriptive purposes, FIG. 5illustrates the output as the shift amount (y_(d)) of the subjectvehicle 40 in the lateral direction. This shift amount (y_(d))represents a shift amount of the subject vehicle 40 after the frontwheels 3 and 4 are steered in accordance with the steering controlamount (δ_(conf)). If there is a disturbance, the shift amountcorresponding to the output of the steering unit 1 will deviatesignificantly from the command value (y_(cr)).

The transfer function, which is a control function for giving thesteering amount for the shift amount (y_(d)), includes a proportionalterm proportional to the command value (y_(cr)) and a feedback (FB) termin response to the difference (Δy) of the shift amount. The proportionalcoefficient of the proportional term is K1. The FB term is to feed backthe detection value detected by a detection unit 60, take the differencebetween the detection value and the command value of the shift amount,and calculate the value of integral for the difference.

The transfer function is represented by the following Expression (1).[Expression 1]δ_(conf) =K1·y _(cr) +K2·∫k _(i) ·Δydl  (1)

Provided that the steering amount when the subject vehicle 40 isattracted to the other vehicle 50 is δ_(p), the steering amount on theopposite side to the direction of being attracted is larger than thesteering amount (δ_(p)), when the following Expression (2) is satisfied.When the subject vehicle is being attracted to a large-sized car, thetire lateral force necessary to cancel the force of being attracted tothe large-sized car is generated, and the travel trajectory of thesubject vehicle is recovered to the target trajectory.[Expression 2]δ_(p)<∫δ_(conf)  (2)

As described in Expression (1), the transfer function includes theintegral term; therefore, the steering amount for the lateral shift(deviation) of the subject vehicle increases with time. Moreover, theintegral term includes the integral increase gain (k_(i)); therefore,the steering amount increases as the integral increase gain (k_(i))increases. Furthermore, the integral term is represented by the integralexpression of the difference (Δy) of the shift amount; therefore, thesteering amount (steering control amount) increases as the lateral shiftamount between the travel trajectory of the subject vehicle and thetarget trajectory increases.

As illustrated in FIG. 6, when the attraction phenomenon occurs, thetravel trajectory M of the subject vehicle expands toward the othervehicle side with respect to the target trajectory C. The targettrajectory C is taken as the center line of the travel lane. An area (S)of the area surrounded by the travel trajectory M and the targettrajectory C is an integrated value per unit time of the shift amount(y_(d)). In one or more embodiments of the present invention, theintegral term includes the integral increase gain (k_(i)>1); therefore,the amount of expansion of the travel trajectory M toward the othervehicle side is small and the area (S) is also small.

In one or more embodiments of the present invention, the steeringcontrol by the lane departure prevention system is performed as thecontrol in ordinary times. In the lane departure prevention system, theintegral increase gain (k_(i)) is set to the ordinary gain. The controldevice 30 detects the state ahead of the vehicle using the camera 12 anddetermines whether or not the passing condition is satisfied. When alarge-sized car is traveling in an adjacent lane ahead of the subjectvehicle and the passing condition is satisfied, the control device 30sets the integral increase gain (k_(i)) to the increased gain before thesubject vehicle actually overtakes the other vehicle. After the integralincrease gain (k_(i)) is set to the increased gain, when the subjectvehicle comes close to the other vehicle and the position of the subjectvehicle is on the side of the other vehicle, the attraction phenomenonis likely to occur.

When the attraction phenomenon occurs, the subject vehicle deviates inthe lateral direction so as to be attracted to the other vehicle. Toavoid being attracted to the other vehicle, the steering wheel 2 isoperated in the opposite direction to the direction of being attracted.The operation of the steering wheel 2 may be operation by automated orautonomous driving or may also be operation by the driver. In thisoperation according to one or more embodiments of the present invention,the integral increase gain (k_(i)) in the lane departure preventionsystem is set to the increased gain and, therefore, the response of thesteering amount to the operation input of the steering wheel 2 is higherthan the response in ordinary times. In other words, the steering amount(steering torque) for giving the steering amount for the operationamount of the steering wheel is larger than the steering amount(steering torque) which is output in ordinary times. Thus, in one ormore embodiments of the present invention, it is possible to predict inadvance that the subject vehicle will be attracted to the other vehicle.The system can therefore execute the steering control for giving thesteering amount (also referred to as “attraction suppression control,”hereinafter) in a short time after the attraction phenomenon occurs.Moreover, when the subject vehicle passes a large-sized car, thefollowability to the target trajectory can be enhanced.

In one or more embodiments of the present invention, the drivingassistance system including the lane departure prevention system (lanekeeping system) may have an automated or autonomous driving function.The automated or autonomous driving includes controlling the steeringangle, the vehicle speed, etc. so that the subject vehicle travels alongthe target trajectory. In the driving assistance system, when the traveltrajectory of the subject vehicle shifts from the target trajectory,such as due to a disturbance, and the subject vehicle deviates in thelateral direction, the steering amount is given in accordance with thelateral shift amount to execute the steering control in an automated orautonomous manner. In one or more embodiments of the present invention,when the subject vehicle departs from the travel lane in a state inwhich the overtaking condition is not satisfied, the steering control isexecuted in an automated or autonomous manner with the response in theordinary control. On the other hand, when the attraction phenomenonoccurs in a state in which the overtaking condition is satisfied, thesteering control is executed in an automated or autonomous manner with ahigher response than the response in the ordinary control.

The driving assistance system including the lane departure preventionsystem (lane keeping system) may not necessarily have an automated orautonomous driving function. For example, a system may be employed inwhich, when the subject vehicle behaves so as to depart from thedetected lane, the driver is notified of the lane departure by a warningdisplay or a warning sound, and when the driver performs the steeringoperation so as to recover to the lane, the steering operation by thedriver is assisted.

FIG. 7 is a graph illustrating the steering amount characteristics.Graphs ‘a’ and ‘b’ represent the characteristics when the attractionphenomenon occurs and the control is executed to avoid being attractedto a large-sized car. The graph ‘a’ represents the characteristic whenthe integral increase gain (k_(i)) is set to the increased gain whilethe graph ‘b’ represents the characteristic when the integral increasegain (k_(i)) is set to the ordinary gain unlike one or more embodimentsof the present invention. The horizontal axis represents time (t). Thevertical axis represents the steering torque. δ_(p) is a steering amountwhen the subject vehicle 40 is attracted to the other vehicle 50.

As illustrated in the graph ‘a,’ when the integral increase gain (k_(i))is set to the increased gain, the steering amount (corresponding to theintegrated value of the steering control amount (δ_(conf))) for givingthe steering amount becomes larger than the steering amount (δ_(p)) atthe time (t₁). On the other hand, when the integral increase gain(k_(i)) is set to the ordinary gain, the steering amount (correspondingto the integrated value of the steering control amount (δ_(conf))) forgiving the steering amount becomes larger than the steering amount(δ_(p)) at the time (t₂>t₁). That is, in one or more embodiments of thepresent invention, because the integral increase gain (k_(i)) isincreased to make the response of the steering amount to the input tothe steering unit 1 higher than the response in ordinary times, the timeuntil the value of integral included in the transfer function ofExpression (1) increases is shortened. As a result, in one or moreembodiments of the present invention, the attraction amount to alarge-sized car can be reduced.

The vehicle control apparatus 100 according to one or more embodimentsof the present invention may be applied to a driving assistance systemsuch as a lane departure prevention system (lane keeping system). Thelane departure prevention system detects a lane using a camera or thelike. When the subject vehicle behaves so as to depart from the detectedlane, the system executes the steering control such that the subjectvehicle keeps the current travel lane. Specifically, the vehicle controlapparatus 100 calculates the steering control amount for giving thesteering amount in accordance with the difference (shift amount) betweenthe current travel trajectory of the subject vehicle and the targettrajectory and outputs the command value to the motor 12. The vehiclecontrol apparatus 100 executes the control of recovering the traveltrajectory of the subject vehicle to the target trajectory by operatingthe motor 12 in accordance with the steering control amount to give thesteering amount in the lateral direction with respect to the travel laneof the subject vehicle. The integral increase gain (k_(i)) in thisoperation is the ordinary gain (corresponding to the ordinary control).

The vehicle control apparatus 100 detects the state ahead of the subjectvehicle using an image captured by the camera 20 and determines whetheror not the passing condition is satisfied. When the passing condition isnot satisfied, the vehicle control apparatus 100 sets the integralincrease gain (k_(i)) in the steering control to the ordinary gain. Onthe other hand, when the passing condition is satisfied, the vehiclecontrol apparatus 100 sets the integral increase gain (k_(i)) to theincreased gain. The vehicle control apparatus 100 calculates thesteering control amount so that, for the shift amount between thecurrent travel trajectory of the subject vehicle and the targettrajectory, the magnitude of the steering amount is larger than that inthe ordinary control. That is, the vehicle control apparatus 100 makesthe response of the magnitude of the steering amount to the shift amounthigher than the response in the ordinary control. Through thisoperation, when the attraction phenomenon causes the subject vehicle tobehave so as to depart from the travel lane, the steering control can beperformed in a short time so that the vehicle keeps the current travellane.

As described above, the vehicle control apparatus 100 according to oneor more embodiments of the present invention executes the control ofrecovering the travel trajectory of the subject vehicle to the targettrajectory, as the ordinary control, by giving the steering amount inthe lateral direction with respect to the travel lane of the subjectvehicle and uses the detection data of the camera 20 to determinewhether or not a large-sized car is traveling in an adjacent lane. Whena determination is made that the large-sized car is traveling in theadjacent lane ahead of the subject vehicle, the response of the steeringamount is increased to a higher response than that in the ordinarycontrol, before the subject vehicle passes the large-sized car. Thisallows the attraction suppression control to be executed in a shorttime.

In one or more embodiments of the present invention, when thelarge-sized car travels in the adjacent lane ahead of the subjectvehicle and the subject vehicle travels on a side closer to thelarge-sized car with respect to the target trajectory of the subjectvehicle, the response of the steering torque is set to a first response,while when the large-sized car travels in the adjacent lane ahead of thesubject vehicle and the subject vehicle travels on a side far from theother vehicle with respect to the target trajectory, the response of thesteering torque is set to a second response. The first response ishigher than the second response. The first response corresponds to theresponse when the integral increase gain (k_(i)) is set to the increasedgain, and the second response corresponds to the response when theintegral increase gain (k_(i)) is set to the ordinary gain.

In one or more embodiments of the present invention, the control flow ofstep 14 includes comparing the shift amount (y_(d)) with the fourthdistance threshold (y_(d_th)) to determine whether or not the subjectvehicle is closer to the other vehicle side than the center line C ofthe travel lane of the subject vehicle (the center line C corresponds tothe target trajectory of the subject vehicle). When the shift amount(y_(d)) is larger than the fourth distance threshold (y_(d_th)), thesubject vehicle is traveling on the other vehicle side of the centerline C; therefore, the integral increase gain (k_(i)) is set to theincreased gain and the torque for the steering torque is set to the highresponse. On the other hand, when the shift amount (y_(d)) is smallerthan the fourth distance threshold (y_(d_th)), the subject vehicle istraveling on the opposite side of the center line C to the othervehicle; therefore, the integral increase gain (k_(i)) is set to theordinary gain and the torque for the steering torque is set to the lowresponse. Through this operation, when the subject vehicle is travelingon the opposite side to a large-sized car on the side, the response ofthe steering torque is the ordinary response, so that the uncomfortablefeeling can be alleviated when the driver steers to the opposite side tothe large-sized car.

In one or more embodiments of the present invention, the lateral shiftamount (y_(d)) between the travel trajectory of the subject vehicle andthe target trajectory is calculated, and the response of the steeringamount is increased to a higher response than that in ordinary times inaccordance with the shift amount (y_(d)). This can enhance thefollowability to the target trajectory when the subject vehicle passes alarge-sized car. Moreover, the steering control amount can be quicklychanged for the attraction amount to the large-sized.

In one or more embodiments of the present invention, when the subjectvehicle has passed the large-sized car, the response of the steeringamount is recovered to the ordinary response of the steering amount.Through this operation, the response can be recovered at the time pointwhen the influence by the attraction disappears.

In one or more embodiments of the present invention, when the passingcondition is satisfied, the integral increase gain (k_(i)) is set to theincreased gain, while when the passing condition is not satisfied, theintegral increase gain (k_(i)) is set to the ordinary gain. This cansuppress the occurrence of frequent correction of steering to the targettrajectory when traveling by the ordinary driving assistance.

In one or more embodiments of the present invention, the value of theintegral increase gain (k_(i)) may be set in accordance with the shiftamount. For example, the control device 30 increases the integralincrease gain (k_(i)) as the shift amount (y_(d)) increases. This canenhance the followability to the target trajectory when the subjectvehicle passes a large-sized car.

In one or more embodiments of the present invention, the determinationas to whether or not the subject vehicle 40 has passed the other vehicle50 may be made not only using the elapsed time (t_(d)) from when thepassing flag is turned on, but also using the inter-vehicle distance.

The control in which the integral increase gain (k_(i)) is set to theincreased gain and then recovered to the ordinary gain will be describedwith reference to FIG. 8. FIG. 8 is a diagram illustrating thepositional relationship between the subject vehicle and another vehicle.As illustrated in FIG. 8, the subject vehicle 40 has passed the othervehicle 50, and the other vehicle is traveling in the adjacent lanebehind the subject vehicle 40. The denotation of the x-axis, the y-axis,and the center point O is the same as in FIG. 4.

The control device 30 specifies a front end Z_(d) of the other vehicle50 from an image captured by the camera 20. The front end Z_(d) is avertex closest to the subject vehicle 40 among vertices on the fourcorners when the other vehicle 50 is viewed from directly above. Asillustrated in FIG. 8, when the other vehicle 50 is traveling on theleft side behind the subject vehicle 40, the front end Z_(d) is a pointpositioned at the upper right when the other vehicle 50 is viewed fromdirectly above. The control device 30 also specifies a rear end Z_(c) ofthe subject vehicle. The rear end Z_(c) is a vertex closest to the othervehicle 50 among vertices on the four corners when the subject vehicle40 is viewed from directly above.

The control device 30 calculates an inter-vehicle distance (x_(ref)) inthe x-direction and an inter-vehicle distance (y_(ref)) in they-direction. The control device 30 compares the inter-vehicle distance(x_(ref)) in the traveling direction with a fifth distance threshold(x_(th_b)) to determine whether or not the inter-vehicle distance(x_(ref)) is larger than the fifth distance threshold (x_(th_b)). Whenthe inter-vehicle distance (x_(ref)) is larger than the fifth distancethreshold (x_(th_b)), the control device 30 determines that the subjectvehicle 40 has passed the other vehicle 50, and recovers the integralincrease gain (10 from the increased gain to the ordinary gain therebyto recover the response of the steering amount to the response inordinary times. On the other hand, when the inter-vehicle distance(x_(ref)) is not larger than the fifth distance threshold (x_(th_b)),the control device 30 determines that the subject vehicle 40 has notpassed the other vehicle 50, and keeps the integral increase gain(k_(i)) at the increased gain.

One or more embodiments of the present invention are not limited togiving the steering amount for the control of the motor 12 in which theopposite torque is output to the steering torque caused by adisturbance. In addition or alternatively, the motor 12 may becontrolled so that the steering torque caused by a disturbance and thetorque by the given steering amount are canceled each other, that is, sothat the torque by the given steering amount is added to the steeringtorque caused by a disturbance thereby to reduce the steering torquecaused by the disturbance.

In one or more embodiments of the present invention, the determinationas to whether or not the subject vehicle 40 has passed the other vehicle50 may be made using a rear camera, side radar, sonar, or the likeinstalled at the rear part of the subject vehicle.

In one or more embodiments of the present invention, the input of theresponse of the steering amount may be made not only by the driver'ssteering operation but also by a control command in an automated orautonomous driving system. That is, when the vehicle is traveling by theautomated or autonomous driving and the subject vehicle passes alarge-sized car on an adjacent lane, the response of the steering amountmay be set by the vehicle control system according to one or moreembodiments of the present invention. Through this operation, it is notnecessary to detect the torque input by the driver to the steering wheel2 and, therefore, the attraction suppression control can be executed ina short time even when the torque input by the driver to the steeringwheel 2 is extremely small or even in an automated or autonomous drivingvehicle in which there is no torque input by the driver to the steeringwheel 2.

DESCRIPTION OF REFERENCE NUMERALS

-   1 Steering unit-   2 Steering wheel-   3, 4 Wheel-   11 Shaft-   12 Motor-   13 Steering angle sensor-   14 Torque sensor-   20 Camera-   30 Control device-   40 Subject vehicle-   50 Another vehicle-   60 Detection unit-   100 Vehicle control apparatus-   1000 Vehicle control system

The invention claimed is:
 1. A vehicle control method for controlling avehicle using a vehicle control apparatus that includes a sensor fordetecting a state ahead of a subject vehicle and a control device, thevehicle control method comprising: executing control of recovering atravel trajectory of the subject vehicle to a target trajectory, asordinary control, by giving a steering amount in a lateral directionwith respect to a travel lane of the subject vehicle; detecting, usingthe sensor, another vehicle that is traveling in an adjacent lane to thetravel lane of the subject vehicle and located ahead of the subjectvehicle; determining whether or not a passing condition is satisfied,wherein the passing condition is one in which the subject vehicle passesthe detected other vehicle; in response to determining that the passingcondition is satisfied, increasing a response of the steering amount ina direction of returning the subject vehicle to the target trajectory toa higher response than that in the ordinary control, before the subjectvehicle passes the detected other vehicle; and in response todetermining that the passing condition is not satisfied, executing theordinary control.
 2. The vehicle control method according to claim 1,comprising: in response to detecting the other vehicle traveling in theadjacent lane ahead of the subject vehicle and the subject vehicle istraveling on a side closer to the detected other vehicle with respect tothe target trajectory, setting the response of a steering torque to afirst response; and in response to detecting the other vehicle travelingin the adjacent lane ahead of the subject vehicle and the subjectvehicle travels on a side far from the detected other vehicle withrespect to the target trajectory, setting the response of the steeringtorque to a second response, the first response being higher than thesecond response.
 3. The vehicle control method according to claim 1,further comprising: calculating a shift amount between the traveltrajectory and the target trajectory in the lateral direction; andincreasing the response of the steering amount to the higher responsethan that in the ordinary control in accordance with the shift amount.4. The vehicle control method according to claim 1, further comprising:when the subject vehicle has passed the detected other vehicle,recovering the response of the steering amount to the response of thesteering amount in the ordinary control.
 5. A vehicle control apparatuscomprising: a sensor that detects a state ahead of a subject vehicle; anactuator that gives a steering amount in a lateral direction withrespect to a travel lane of the subject vehicle; and a controller thatcontrols the actuator, the controller configured to: calculate a controlsteering amount for the actuator to generate the steering amount inaccordance with a shift amount in the lateral direction with respect tothe travel lane of the subject vehicle; execute control of recovering atravel trajectory of the subject vehicle to a target trajectory, asordinary control, by operating the actuator in accordance with thecontrol steering amount; detect, using the sensor, another vehicletraveling in an adjacent lane to the travel lane of the subject vehicleand located ahead of the subject vehicle; determine whether or not apassing condition is satisfied, wherein the passing condition is one inwhich the subject vehicle passes the detected other vehicle; when thepassing condition is satisfied, control the actuator to increase aresponse of the steering amount in a direction of returning the subjectvehicle to the target trajectory to a higher response than that in theordinary control, before the subject vehicle passes the detected othervehicle; and when the passing condition is not satisfied, executing theordinary control.